Rapid prototyping and manufacturing system and method

ABSTRACT

A stereolithography apparatus having a resin vat with resupply containers in one-way flow communication and a leveling container in two-way how communication, an automatic offload cart to remove and replace build support platforms, an elevator assembly for supporting and releasably retaining a build platform removably attached to the stereolithography apparatus frame such that elevator forks supporting the build platform can be released into the vat and removed from the stereolithography apparatus with the vat, and a recoater assembly and recoater blade for mapping the resin surface in the vat and applying a fresh coating of resin to a cross-section being built in the vat.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/240,820, filed Sep. 30, 2005, now U.S. Pat. No. 7,690,909, which ishereby incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

This invention relates to methods and apparatus for rapid prototypingand manufacturing (“RP&M”) to produce three-dimensional objects, andmore particularly to improving the productivity and efficiency of RP&Msystems.

RP&M is the name given to a field of technologies that can be used toform three-dimensional objects or solid images. In general, RP&Mtechniques build three-dimensional objects, layer-by-layer, from abuilding medium using data representing successive cross-sections of theobject to be formed. Computer Aided Design and Computer AidedManufacturing systems, often referred to as CAD/CAM systems, typicallyprovide the object representation to an RP&M system. The three primarymodes of RP&M include stereolithography, laser sintering, and ink jetprinting of solid images.

Laser sintering builds solid images from thin layers of heat-fusiblepowders, including ceramics, polymers, and polymer-coated metals towhich sufficient energy is imparted to solidify the layers. Ink jetprinting builds solid images from powders that are solidified whencombined with a binder. Stereolithography, to which the subject matterherein is primarily addressed, builds solid images from thin layers ofpolymerizable liquid, commonly referred to as resin.

Stereolithography and laser sintering systems typically supply theenergy for creating and building up the thin cross-sections ofthree-dimensional objects through modulation and precise directionalcontrol of lasers. The laser applies energy to a targeted area of thelayer of powder or liquid building medium. The thin targeted layer iscalled the working surface of the building medium. Conventional RP&Mlaser systems position the laser beam using a scanning system havinggalvanometer-driven mirrors that are directed by a control computer. Themirrors deflect a laser beam in response to a CAD/CAM program that hasbeen tessellated into the STL format and sliced into cross-sectionaldata files that are merged into a build file.

In stereolithography, three-dimensional objects result from successivesolidification of a plurality of thin layers of a polymerizable liquid,one on top of another, until all of the thin layers join together toform the three-dimensional object. Each layer represents a thincross-section of the desired three-dimensional object. Polymerizableliquids are generally referred to as “resins,” and solidified layers ofresin are said to be cured. Practical building media typically includeresins that cure sufficiently fast, usually with ultraviolet light. Anultraviolet laser generates a small and intense spot of light that ismoved across the liquid surface with a galvanometer mirror in an x-yscanner in a predetermined pattern. The scanner is driven by computergenerated vectors or the like. This technique rapidly produces precisecomplex patterns.

A typical stereolithography system includes a laser scanner, a vat forcontaining the resin, an object support platform, which is capable ofbeing raised and lowered in the vat, and a controlling computer. Thecomputer controls the system automatically to make a plastic part,forming one thin cross-section of cured resin at a time on the objectsupport platform and building the desired three-dimensional object uplayer-by-layer. The object support platform supports the cured layersand rests beneath the surface of the liquid resin the distance of onelayer thickness to define a working surface. The laser cures selectedportions of liquid resin at the working surface to cure the next layer.The computer controls the system to recoat the surface of the curedresin with fresh resin and repeats the steps thousands of times untilcompleting the desired object. The object or multiple objects beingbuilt and the completed sequence of steps is sometimes referred to as a“build.” An operator removes the build from the vat of resin forcleaning and further curing as needed. The liquid resin remaining in thevat remains usable so long as it is not too contaminated with suspendedbits of cured resin.

One method of recoating the cured resin layers with fresh resin requires“deep dipping” the platform in the liquid resin. The platform verticallydrops below the surface of the bath of resin a distance greater than thedesired layer thickness to coat the cured layers with fresh liquidresin. The system raises the platform to one layer thickness beneath theresin surface. Excess liquid resin runs off to level the resin bygravity to a single layer thickness. Thereafter, the laser appliesenergy to the working surface.

The waiting period for the thin layer to level varies depending onseveral factors, including the viscosity of the polymerizable liquid,the layer thickness, part geometry, cross-section, and the like. Somerecent resins level more quickly than prior resins. Leveling can beassisted by the use of a doctor blade or vacuum assisted doctor blade,sometimes referred to as a Zephyr blade, to sweep across the surface ofthe resin, applying fresh resin and removing the excess much morequickly than by gravity settling and leveling the working resin surfacein the vat containing the resin. The blade is said to recoat thesolidified layers and is often referred to as a “recoater.”

Various improvements have been proposed to increase the efficiency withwhich RP&M techniques are accomplished, including improvements to lasersystems for more efficient use of the laser and for more preciseimaging, improvements to building media, reduction of curing time,control of resin level in the vat, and the like. It would be desirableto make additional improvements that enable stereolithography systems toproduce more objects in less time, and to do so with greater precisionand less human intervention.

SUMMARY

This invention provides several improvements to rapid prototyping andmanufacturing systems that enable an unattended building of athree-dimensional object. Two three-dimensional objects can be built insequence, one after the other, from the same location in a singlebuilding medium, without requiring a human operator present afterbuilding the first object starts. The system does not require anoperator to attend the completion of the first build and its removalfrom the building medium, the start of the second build, or thecompletion of the second build. While the system can be used for asingle build, the system allows the return of an operator to a systemhaving two objects built in sequence and awaiting unloading, cleaning,and further curing as needed.

The system of the invention can be applied to multiple chamber unitshaving a single energy source so that more than one build can becompleted at a time, each followed by a second unattended build. Theobjects completed in a single first build and those completed in asecond build can be of the same or different design, and the buildingmedium is the same for the second build as for the first. The objectscompleted simultaneously in adjacent chambers, which will be either thefirst or second build in an unattended build sequence, will usually beprepared from the same building medium, but need not be so long as theappropriate machine and process adjustments are made to enable curing.

In more specific detail of an embodiment of the invention, the inventionprovides apparatus and methods for stereolithography that include ahousing having an elevator for supporting, raising, and lowering asupport platform for an object to be built, a vat for containing aliquid resin from which an object is built, a source of energy forsolidifying selected laminae of the liquid resin, a cart forunattendedly removing a first build from the elevator, and controlsystems for controlling the elevator, the energy source, the cart, andthe resin level in the vat.

In a more specific embodiment, the elevator component includes anelevator attachment bracket for attachment to an elevator drive plate inthe stereolithography housing. The attachment bracket has hooks forreleasably engaging attachment to a support rod on the elevator driveplate and a receiver for receiving a centering pin on the elevator driveplate that locates the attachment bracket precisely in alignment withthe horizontal x, y plane of the working surface of the resin.

The attachment bracket is fixedly supported on an elevator frame thatextends vertically so as to be readily lowered into the resin vat andraised out of the vat. The elevator frame also extends generallyhorizontally for providing a pair of elevator forks to support andsecure an object support platform. The object support platform issupported by the forks, and by arms extending horizontally outwardlyfrom each side of the rear of the forks. The platform is secured to theforks by releasably engaging latch members at the front of the forks.The latch members are actuated by a spring-biased latch linkage. Thelatch linkage is operable to engage a ramp on the elevator support whenthe elevator is raised sufficiently high above the resin so as torelease the latch members, and thus the platform, from latchingengagement.

The cart for removing a first build from the elevator can, if desired,be operated by computer control to install a fresh object supportplatform on the elevator. The support platform can be lowered into thevat for a second, unattended build. After the build is completed, theelevator rises to remove the completed three-dimensional object orobjects in the build and the platform from the resin to drain. The cart,referred to below as an auto off-load cart, is equipped to dockprecisely into the housing and with the resin vat. Telescoping armsextend on computer-controlled command to engage and remove the firstbuild and associated support platform and can be extended to install afresh platform for a second build, if desired.

The resin vat includes containers of supplemental resin for supplyingadditional liquid to the vat as needed in response to a level sensor.During a build, it is desirable to maintain a precisely controlled levelof liquid in the vat. The resin level fluctuates as some of the resin issolidified and as the platform lowers the build into the resin tocomplete additional layers at the surface. It is also necessary to addresin to the vat between builds to maintain the level of resinsufficient for a second build.

In a specific embodiment of the invention, the vat and supplementalresin containers include tags for radio frequency identification (RFID).The resin in the supplemental container can readily be screened andidentified prior to entering into the resin in the vat so as to avoidcontamination of the resin in the vat by the wrong resin.

In still further embodiments, the invention includes a recoater assemblyfor leveling the resin that can be computer controlled for remainingparallel to the working surface across the surface of the resin. Therecoater assembly includes a recoater blade and a carrier for the bladethat makes adjustments in any of three directions (y, z, and theta): 1)the horizontal y-axis direction of travel of the recoater assemblyacross the resin surface, 2) the vertical z-axis of travel up and down,providing for blade gap between the bottom of the recoater blade and theworking surface of the resin and for removal of the recoater assemblyfrom the vat, and 3) the rotational theta axis, parallel to the y-axis,for maintaining the blade parallel to the resin surface throughout they-axis direction of travel. The x, y plane corresponds to the workingsurface of the resin.

The recoater blade is kept at the same distance from the working surfaceof the resin throughout the length of travel of the recoater. Therecoater blade travels vertically along an axis “z” and also rotatesabout a longitudinal axis, theta, that is parallel to and spaced fromthe axis “y” of travel of the recoater so that the ends of the recoaterare always the same distance from the resin surface and the blade isparallel to the resin surface. This embodiment of the invention correctsfor machine errors and reduces inaccuracies in the three-dimensionalproducts. Machine errors arise from unevenness in the mechanical systemsthat in the past have required tedious adjustments to the recoatersystems.

Computer control of the recoater is provided in response to data setsfor the distance between the bottom of the recoater and working surfaceof the resin obtained prior to initiating laser contact with the resinsurface. A sensor contained within the recoater carrier housing providesthis data to the computer. The sensor is on a motion system that movesalong the length of the blade (x-axis). The sensor operates above thehorizontal x, y plane of the working surface of the resin at two fixedlocations x, one on each side of the recoater adjacent the edge of thevat, to obtain data at multiple points y of travel of the recoater. Therecoater has thinned-down feet at each end, blade gap sensing feet, towhich the sensor determines the distance. The distance of the sensor tothe bottom of the foot can be accurately determined since the distanceto the bottom of the foot is known and can be added to the sensordetermination of the distance to the top of the thinned-down portion ofthe foot. The sensor is displaced a slight distance x to obtain areading of distance to the working surface of the resin. The differencebetween the distance to the working surface and the bottom of therecoater is calculated and this data is stored for each side of theresin vat. The computer sets the blade gap for the z axis based onempirical data for the particular resin in use. The recoater is rotatedabout the theta axis and is raised or lowered along the z axis tomaintain a constant distance at each end from the working surface sothat the blade gap remains fixed. Thus, machine and positioning errors,including errors in the tracks along which the recoater travels, can betaken into account and corrected.

The recoater does not need to be changed between builds in theunattended sequential build mode and is designed for precise positioningand easy removal and replacement by hand and without tools. The recoateris fixedly attached to the carrier at each end. Magnets may be used.

Correct orientation of the blade is confirmed in two ways. Differentlyshaped alignment pins are included on each end of the blade forplacement in corresponding receptacles on the recoater carrier housing.Contacts are included on each end of the recoater carrier, all of whichmust be activated to result in a signal from a proximity switch to showthe blade is correctly positioned on the carrier housing. The recoaternormally is vacuum-assisted and is provided with a vacuum receptacle inthe blade, a countersink for a soft fitting extending from the carrier,for which vacuum communication is established simply by correctlypositioning the blade on the carrier and turning on the vacuum.

The apparatus and process of the invention can be applied to a singlevat of resin or to two or more vats operated with a single laser inwhich one layer is solidified in selected vats while others arerecoated. Typically, two vats will be lased, one after the other, and itis possible to lase more than two using appropriate scanners and beamsplitters.

Thus, the invention provides for an unattended stereolithographic buildfrom a single vat of resin after a first build has been completed. Theinvention includes a number of improvements to stereolithographyapparatus so as to enable unattended builds and provides severalfeatures that can be subject to automated computer control to greatlysimplify obtaining the precision required for accurate production ofthree-dimensional objects. These improvements include the automatedoff-load cart for removing a first build from the elevator and providinga fresh object support platform, switching the laser between vats forsimultaneous builds, coupling of supplemental resin containers directlyto the stereolithography system for automated determination of resinsupply sufficiency to support an unattended build, RFID identificationof resin containers for maintaining integrity of the resin, automatedleveling of the resin working surface level during a build and automatedrefilling of the vat between builds, automated determination of thedistance between the working surface and the recoater and the mapping ofthis distance over the axis of travel of the recoater for automatedcontrol of the rotation of the recoater and correction of machineerrors, automated release of the object support platform from theelevator and replacement with a fresh platform, and installation andremoval of the recoater blade entirely by hand and in the absence oftools.

BRIEF DESCRIPTION OF THE DRAWINGS

Haying thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a perspective view of a dual-chamber housing of the inventionfor producing objects by stereolithography and showing the resin vatsassociated therewith, one in shadow and one in perspective;

FIG. 2 is a perspective view of a resin vat showing disposed thereon inan exploded view, an object support platform and a subassembly of theelevator for raising and lowering the platform in the resin;

FIG. 3 is a perspective view of a portion of the elevator subassembly ofFIG. 2 having portions removed therefrom to show various details of theelevator subassembly;

FIG. 4 is a perspective view of a recoater assembly of the invention;

FIG. 5 is an exploded partial perspective of a recoater carrier andrecoater blade for one end of the recoater assembly of FIG. 4;

FIG. 6 is a partial perspective view of the underside of the recoaterblade portion of FIG. 5;

FIG. 7 is a partial perspective view of the interior rear of astereolithography chamber of the invention and showing a portion of asubassembly of an elevator;

FIG. 8 is a partial perspective and isolated view of the elevatorsubassembly of FIG. 7 and showing its relationship to a portion of theelevator subassembly of FIG. 2;

FIG. 9 is a partial perspective view of the elevator subassemblies ofFIGS. 2 and 8 shown assembled;

FIG. 10 is a partially cut-away view of a portion of the chamber housingshowing the axes of movement of the elevator, which is the vertical zaxis, of the recoater blade and carrier, which is the horizontalfront-to-rear y axis, and of a blade gap sensor, which are the y axisand the horizontal side-to-side x axis;

FIG. 11 is a sectional side view showing the resin cart entering intothe process chamber;

FIGS. 12 through 14 are a series of sectional side views showing theresin cart in position in the process chamber and attached to theelevator, and elevation of the platform;

FIG. 15 is a highly schematic perspective view of the recoater assemblytraversing the resin surface and a sensor obtaining readings formaintaining blade gap;

FIGS. 16A, 16B, and 16C are side views showing the recoater assemblyisolated above the resin surface and obtaining readings for maintainingblade gap;

FIG. 17 is a highly perspective view showing the relation of the laserscanner and movement of the recoater assembly across the vat;

FIG. 18 is a perspective view showing evaluation of thestereolithography laser beam's spot size, focal length, and power in anextreme position;

FIG. 19 is a perspective view showing application of a laser beam tosolidify a layer of resin;

FIGS. 20 and 21 are sectional side views of the perspective of FIG. 19and show various stages of build completion of a single object build;

FIGS. 22 and 23 are, respectively, a sectional side view and aperspective view of the built object and platform raised above the levelof the resin to the unload position;

FIGS. 24 through 31 are a series of side views showing operation of theauto off-load cart, including completion of the first build, removal tothe cart, installation of a fresh platform, completion of the secondbuild, and removal of the second build from the vat;

FIG. 32 is a perspective view of a resin vat of the invention withresupply resin containers and a level maintenance container mountedthereon; and

FIG. 33 is a flow diagram showing the steps broadly taken in completinga second and unattended build.

DETAILED DESCRIPTION

The invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. These embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the invention to those skilled in the art.

Turning now to FIG. 1, shown generally at 10 is a dual-chamber housingfor housing two chambers 12, 13 for stereolithography. The housing hastwo chambers for increased efficiency of laser usage. While the objectsurface in one chamber is recoated, the laser can be applied to therecoated object surface in the other chamber so as to build objects inboth chambers in a single run. The laser and the system for using thebeam in multiple chambers is addressed in detail below.

The housing has view windows 14, 15 on opposite side walls, one in eachchamber 12, 13, respectively. Each chamber has a door 16, 17 with ahingedly openable and removable window. The windows are used foroperating an automated system for unattended removal of a supportplatform and completed object and placement of a fresh object supportplatform for a second and unattended build.

Vat 21 contains a resin 18 from which the stereolithography apparatuscreates three-dimensional objects. Vat 20 is shown in shadow disposed inchamber 12. Vat 21 is shown ready to introduce into chamber 13 throughopen chamber door 17. An elevator attachment bracket 23 is locatedadjacent the rear of the vat 21 for attachment to an elevator lift plate82 (FIG. 8) enabling an object support platform 30 (FIG. 2), which isthe platform on which the build takes place, to be raised and lowered inthe vat with respect to the working surface of the resin. The elevatorattachment bracket has hooks 86 (FIG. 8) by which attachment to the liftplate is secured.

The elevator attachment bracket and elevator lift plate cooperate aspart of an elevator assembly that comprises several components all ofwhich cooperate to lift and lower the platform. FIG. 2 shows disposedabove vat 21 a subassembly 22 of the elevator components that can beintroduced into and removed from the chamber with the vat. If desired,the removable subassembly shown in FIG. 2 can be dedicated to a singlevat. These components include the elevator attachment bracket 23 rigidlyfixed to a supporting elevator framework 24 and elevator forks 25supported on frame 24. Frame 24 extends vertically so as to be capableof reaching the bottom of the vat. The forks on the frame cooperate withspaced supports 27, 28 extending laterally from the rear of the frame tosupport build platform 30. Latch 36 works with tabs 33 and 35 on theforward end of the elevator framework to secure and release the platformfor automated installation and removal of the platform once the buildhas been completed and the elevator has been lifted from the vat.

It should be recognized that the above discussion of FIGS. 2 and 8 withrespect to the elevator assembly and the subassembly 22 associated withvat 21 and chamber 13 applies equally to vat 20 and chamber 12 and thatvat 20 will have similar elevator components and an object supportplatform. In this regard, the discussion below of the elevator assemblyand subassemblies, recoater assembly, vat, process steps, and operationof the auto off-load cart in the context of one vat or chamber appliesequally to another vat or chamber.

FIG. 3 shows the frame 24 and elevator forks 25 for supporting platform30 with sheet metal covering removed and exposes a latch linkage 37.Latch linkage 37 is operable to actuate latch 36 to secure the platformin conjunction with tabs 33 and 35 on installation and to release theplatform from the forks for removal from the system. The latch linkageis actuated by a spring biased rod 38 to cause 36 to secure the platformto the forks when installed on the forks and then release the platformfor removal when the platform is sufficiently elevated above the vat.

Actuation of the latch linkage for release of the build platform fromthe elevator forks is illustrated in FIG. 9 with reference to FIGS. 22and 23. FIG. 9 shows the platform 30 secured to the elevator forks 25within the chamber 12 and within vat 20 within the chamber. When theelevator assembly is raised sufficiently high, rod 38 engages a rampsurface 90 on a chamber component frame 92 (FIGS. 3, 9, 22, and 23). Asthe elevator continues to rise, the ramp forces the latch release rodoutwardly toward the platform and actuates the latch linkage to releaselatch 36. Similarly, when a platform is installed on empty forks and theelevator assembly is lowered so that the ramp does not engage therelease rod, then a spring biases the latch release rod and linkage toclose the latch and secure the platform against tabs 33 and 35 on theforks (FIGS. 28 and 29).

FIGS. 7 and 8 illustrate in detail a second subassembly 39 of componentsof the elevator assembly. FIG. 7 illustrates the subassembly in thecontext of the stereolithography chamber and FIG. 8 illustrates thesubassembly in relation to the elevator attachment bracket 23 of thefirst subassembly. These components of the second subassembly are fixedin stereolithography chamber 12 along the back wall 80 (FIG. 7) oppositedoor 16 (FIG. 1) and do not enter or exit with a vat as do thecomponents of the subassembly 22 shown in FIG. 2. These fixed elevatorcomponents of the second subassembly of FIGS. 7 and 8, the chamberelevator components, receive the elevator components of the firstsubassembly, the vat elevator components (FIG. 2), and specifically theelevator attachment bracket 23 of FIG. 8, to form, in combination, anentire elevator assembly. The elevator assembly with the twosubassemblies connected is shown in FIG. 9 in a perspective view.

Elevator lift plate 82 includes a locating pin 83 for fitting into areceiver 96 of FIG. 9 on elevator attachment bracket 23, locatingattachment bracket 23 and thereby the elevator frame 25 and forks 24 inthe horizontal x, y plane. The elevator lift plate 82 includes a rod 84that engages the hooks 86 on the attachment bracket 23 (FIG. 8) forraising and lowering the attachment bracket and associated frame andforks within and out of a vat of resin. A lift screw 85 is shown inFIGS. 7 and 8 for the elevator lift plate 82. Lift screw 85 is turned bymotor 91 to lift and lower the elevator lift plate, attachment bracket,frame, and forks along the vertical z axis. Also included is a locatingpin 88 for locating the resin vat 20 in a horizontal plane parallel tothe x, y plane of the surface 112 of resin 18 (see briefly FIG. 12).

FIG. 10 illustrates in partial perspective the elevator lift plate 82positioned on the z axis to receive a vat of resin in stereolithographychamber 12 and the positions in relation thereto of the laser scanner100 and recoater blade and carrier, 42 and 44 respectively. The sequenceof steps of rolling a vat into a stereolithography chamber and preparinga build are shown in FIGS. 11 through 23. As a vat with its elevatorsubassembly and secured platform are rolled into a stereolithographychamber of the invention and centered on locating pin 88, then theattachment bracket 23 is aligned vertically with the elevator lift plate82 and lift rod 84 (FIGS. 11 and 12). Motor 91 turns lift screw 85 toraise the elevator lift plate (FIG. 13). As the lift plate rises, thelift rod engages and seats in hooks 86 on the attachment bracket 23(FIG. 13) and locating pin 83 engages and seats in receiver 96 (seebriefly FIG. 8) on the attachment bracket, thereby joining the chamberelevator and vat elevator subassemblies and centering the vat elevatorsubassembly within the vat. As the lift plate rises farther still, thevat elevator subassembly and platform rise within the resin (FIG. 14.).Raising the lift plate sufficiently releases the latch 36, as discussedabove. Lowering the lift plate sufficiently releases the lift rod fromengagement with the attachment bracket so that a vat and vat elevatorsubassembly can be removed, if needed. Normally, the vat is removedseparately from a platform having a build upon it.

Turning now to a discussion of the recoater assembly and its use formapping the blade gap prior to a build, FIG. 15 illustrates a sectionalview through chamber 12 of a recoater blade 42 and carrier 44 traversingthe resin working surface 112 in the y direction. The recoater assemblyis identified generally at 40 (FIG. 4). The recoater assembly includes arecoater blade 42 and a carrier 44 to which the recoater blade isattached and which provides for movement of the recoater blade. Therecoater blade is computer controlled to move along the axes asshown: 1) horizontally back and forth across the surface of the resin,in the y axial direction, 2) vertically up and down in the z axialdirection, and 3) rotationally about the center of the blade, which isthe axis theta, parallel to and spaced from the y axis. A conventionalfunction of a recoater blade and of the one illustrated is to speed upleveling of fresh resin layers between laser scanning exposures of theworking surface 112, which typically provides parts of greater accuracyin a shorter period of time than deep dipping and gravity settling.

The carrier for the recoater blade of FIG. 4 is mounted to a verticalmotion stage 47. Vertical motion stage 47 sits in a track 49 fortranslating the blade in the up and down direction along the vertical zaxis. Track 49 in turn mounts into track 50 and travels in track 50 toadvance the recoater blade across the surface of the resin, in thehorizontal y axial direction. Cable drives and associated stepper-basedlinear actuator motors have been determined to be suitable for use inthese aspects of the practice of the invention.

The recoater assembly of the invention includes a sensor 45 forproviding readings to a controller to keep the recoater blade parallelto the resin surface throughout its length of travel. Each end of therecoater blade is kept at the same distance from the resin surface. Thesensor is contained within carrier 44 and is translatable in the x axialdirection along the length of the carrier so that distance readings canbe obtained in different locations along the x axis of the surface ofthe resin. A cable drive contained in the carrier can be used totranslate the sensor in the carrier, powered by a motor in the verticalmotion stage 47.

The distance of the recoater blade from the resin surface when sweepingacross the surface is termed “blade gap.” The blade gap typicallydepends on the resin chosen for the particular build and its physicalcharacteristics, and is a quantity that is empirically predetermined forthe build and stored in the stereolithography control computer's memory.The function of the sensor 45 is to provide the data necessary to keepthe blade gap as specified throughout the range of travel of therecoater blade across the resin surface. Variances in the tracks inwhich the recoater assembly travels and other sources of machine errorcan change the blade gap. The computer controlled recoater assembly ofthe invention substantially resolves these problems, taking what hasbeen a hardware problem in the industry and providing a softwaresolution.

Sensor 45 is a laser diode sensor and is a high resolution sensor with anarrow measurement range. An Omron optical sensor Model No. ZXLD30,available from Omrom Electronic Componentsin Schaumberg, Ill., has beendetermined to be useful as the sensor 45. The Omron sensor is highlysensitive and works by emitting a focused energy beam to contact thetarget and then receiving the reflected beam, from a comparison of whichdistance to the target can be determined with a degree of accuracysufficient for stereolithography.

The recoater blade 42 is kept parallel to the resin surface in responseto data obtained by the Omron sensor 45 prior to the start of a build.The sensor obtains data from which the computer controller determinesthe distance from the bottom 76 (FIG. 6) of the recoater blade to thetop or working surface 112 (FIG. 12) of the resin along a variety ofpoints y at two points x along each side of the resin vat correspondingto the two ends of the recoater blade. FIGS. 4, 5, 6, 15, 16A through16C, and 17 illustrate interaction between the Omron sensor and therecoater assembly to obtain this data and map the adjustments to therecoater blade that will be made during a build. During a build, thecomputer controller rotates the recoater blade, in response to the mapobtained prior to the build, about its axis of travel, theta, which isan axis parallel to and spaced from the y axis of the resin surface, tokeep the two ends of the recoater blade the same distance from the resinsurface at spaced points x along the y axis. The data based on which theblade is rotated is not obtained in real time, and the differencebetween real time data and a map obtained prior to the start of a buildhas not been determined to be significant.

FIGS. 5 and 6 show an end portion of the recoater blade 42, taken alongthe x axis and corresponding to the right hand end of the recoater bladeillustrated in FIG. 4. FIG. 6 shows the same end as FIG. 5 and from thebottom of the blade to fully illustrate the blade's features. Feet 56,only one of which is shown, extend laterally outwardly from the bottomof the blade on each end, the bottom surface of which, surface 60,defines the bottom of the blade for measurement purposes. Each foot iscut down or precision ground to a thin surface 58 on the end of the footaway from the blade at the top surface for obtaining the Omron sensorreadings for the bottom of the blade. The distance from the bottom ofthe foot, 60, to the top surface of the cut down portion, 58, is fixedand stored in the computer. This foot depth distance is small owing tothe operating range of the Omron sensor.

To obtain readings, the Omron sensor is set within the carrier at apoint along the x axis, adjacent to one end of the recoater blade. FIGS.4, 15, and 16A through 16C show the sensor 45 in shadow in the carrieradjacent the left end. The blade does not touch the resin when obtainingreadings and no resin obscures the top of the foot from the Omronsensor. As shown in FIG. 15 in the context of the chamber and in FIG.16A in a detailed view, at a fixed location x, y, the Omron sensor 45takes a reading of the distance from the sensor to the top 58 of thefoot 56 to assign a value for the foot position corresponding to thebottom 60 of the foot and based on the predetermined depth of the footbetween the surface 58 and bottom 60. As shown in FIG. 16B, at the samelocation y as in FIG. 16A, the Omron sensor is displaced a smalldistance x to approximate the same location x as the foot and sufficientto enable the Omron sensor to take a reading from the sensor to the topof the resin surface, 112. The computer control determines thedifference between these two readings for the bottom of the foot and theresin surface and stores the datum. As shown in FIG. 16C, the recoaterassembly then translates a distance y as indicated by the arrows toobtain additional data points until the entire surface along one side ofthe vat has been mapped at a variety of points y for one x. Thereafter,the Omron sensor translates to the opposite side of the carrier, theright side, to obtain data mapping that side of the vat at differentlocations x and the same locations y to complete the map. The entire mapis obtained by computer control and stored for use during the subsequentbuild.

The recoater blade 42 can be attached to and removed from the carrier 44entirely by hand. The stereolithography system's computer controlsalignment of the recoater blade and substantially reduces the tediousprocedures associated with prior apparatus. Turning now to FIGS. 5 and 6and a discussion of the features of the recoater blade and carrier thatprovide for ease of installation and removal of the blade, knurledhandles 55, only one of which is shown on the recoater blade of FIG. 6are used for installing the recoater blade and removing the recoaterblade from the carrier by hand. It should be recognized that there is acorresponding handle on the end of the blade not illustrated in FIG. 6,as can be seen in FIGS. 4 and 17 through 19. A receiver 64 on therecoater blade (FIG. 5) receives a corresponding alignment pin 66 on therecoater carrier. Pin 66 is illustrated round in cross-section and thisshape can be varied. It may be desirable to provide a second alignmentpin of a different shape on the opposite end of the recoater carrier anda corresponding receiver on the blade. These alignment pins assist theoperator to make sure the blade is correctly oriented on the carrier.Magnets 70 and 71 or other attachment means, one at each end of theblade carrier and one at each end of the recoater blade, respectively,secure the recoater blade on the carrier. Other attachment means can beused, although these may require tools for installation or removal ofthe blade. Contacts 72 can be provided to activate a proximity switch 75for indicating that the blade is properly secured in place on thecarrier. It is useful to provide three such contacts, one on the end ofthe carrier as shown, and two on the opposite end so that a three-pointcontact is required to activate the proximity switch to signal correctposition for the recoater blade on the carrier.

The recoater blade includes a vacuum channel 77 on its bottom surface 76seen in inverted position in FIG. 6. The vacuum channel aids in levelingthe fresh resin layers in a conventional manner. The blade includes acentrally located sight window 78 (FIG. 4) for sighting by an operatorwhether the vacuum is activated. The vacuum connection between the bladeand carrier is not hard plugged and requires no tools to complete. Thevacuum connection is “soft” in that connection is provided betweencooperating and sealing vacuum ports located centrally of the blade andcarrier, typically a vacuum cup on the blade and a cooperating member onthe carrier.

Prior to installation of the vat in a stereolithography chamber, therecoater assembly is “parked,” which is to say the recoater blade islocated on the y axial direction nearest the door of the chamber and israised in the z axial direction out of the way of the vat which haswheels affixed to its bottom so it can be maneuvered like a cart (FIGS.11 and 12). The vat can be rolled into the chamber without striking therecoater assembly. Once the vat is installed, the recoater assembly canbe lowered adjacent to and spaced from the surface of the resin formapping the relationship between the resin surface and the bottom of therecoater blade (FIG. 17). The invention accomplishes mapping with therecoater blade held a greater distance above the resin working surfacethan the blade gap, a distance sufficient to make sure the feet on theblade do not become covered with resin, which would negatively impactthe ability of the Omron sensor to develop the data needed to controlthe blade gap.

When a build begins, the recoater blade vacuum is turned on and theblade is lowered to the predetermined blade gap for the resin (FIG. 14).The vacuum pulls resin up into the vacuum channel 77 in the blade andinto the sight window 78. The feet typically will have resin over themas the blade sweeps the surface, which can occur for each application ofa fresh resin layer to the build on the platform.

The accuracy of the build is very sensitive to maintaining a preciselevel of the resin in the vat. The build plane is established prior tothe start of a build. The laser scanning system 100 (FIG. 19) is rigidlymounted to the chamber and is controlled to strike the resin workingsurface at a particular point in space, termed the “build plane,” whichestablishes the range of z values in which the x, y plane of the workingsurface can be located. The ability of the invention to automateeffective leveling of the recoater blade depends on keeping the resin atthe same level as when the map of the resin surface was establishedprior to the build.

A second Omron liquid level sensor is shown at 87 (FIGS. 7 and 9) and isrigidly fixed to the elevator frame in the rear of the chamber housingfor determining the level of resin in the vat and whether additionalresin should be added to the vat. Sensor 87 determines whether resinneeds to be added or removed to maintain a build plane during a build.During the build, the sensor (FIG. 30) determines the level of resin inthe vat so that resin can be added or removed to maintain the same levelat all times and thus at the same distance from the blade as thatobtained during mapping. The Omron sensor is a laser diode sensoroperating closed loop in that the sensor operates between successivescans by the laser of the working surface and shuts off when theappropriate resin level is reached.

A vat 21 with supplemental resin containers 127, 128, 129 for use incontrolling the resin level is illustrated in FIG. 32 with a removablecover 141. Resin containers 127, 128 and 129 are retained in tiltablereceptacles 133, 134 and 135 respectively which are pivotable away fromvat 21 by engaging handles 136, 137 and 138 to facilitate ease ofinstallation and removal. Each container 127, 128, and 129 connects tovat 21 via a quick disconnect double shut off coupling. Each container127, 128, and 129 has a nozzle that mates with a coupling (both notshown) inside the corresponding receptacle 133, 134, and 135 on vat 21so that when connected resin is able to flow from the container throughthe coupling into the vat 21. Each nozzle has molded or otherwiseintegrated into it an RFID tag. Each coupling is a “smart coupler”because it has molded or otherwise integrated into it a reader to senseand pass on to the stereolithography system's control computer dataabout the container and resin in it, such as resin type, resin batchnumber, expiration date, resin volume and potentially the vat andstereolithography system identities in which the container is beingused. The readers are proximity readers so the stereolithographysystems' control computer can alert the operator with an alarm beforethe container nozzle is couplingly connected to the vat via thereceptacle coupling if the incorrect resin or an expired resin is beinginstalled in the container. This data flow between the vat and thestereolithography system's computer occurs through the data and powerport 101 when the vat and the stereolithography system are connected viaappropriate cabling. Each container can also track the amount of resinthat flows from it into the vat. Two of the supplemental resincontainers, 127 and 128, refill the vat between builds and operatethrough bellows pump 102 to supply a sufficient stroke volume of about aliter of resin per minute for a 420 liter capacity vat. Two Omronultrasonic sensors (not shown) mounted on a wall of the vat 21 determinewhether the resin is within preselected minimum and maximum values priorto a build to signal whether resin needs to be added. Each vat 21 alsohas an RFID tag 19 on the outside wall on which the elevator attachmenthooks 86 of FIGS. 11 and 12 are supported which is read by a reader 81,and passes the data about vat identify, initial resin quantity, and dataof installation on to the stereolithography system's control computer.

Resin is supplied first from one container, for example 128, via line106 and when that container is emptied, from the other container, forexample 127, via line 107 by the valve assembly 131 having theappropriate valve opened by the stereolithography control computer inresponse to the sensing from the ultrasonic sensor that the resin isbelow the minimum level prior to the start of a build. Replenishingresin flows from the supply container through valve assembly 131 andsupply line 111 to the bellows pump 102 via an inlet port and through anoutlet port (both not shown) to vat 21. The other of the containers,129, acts as a reservoir via inlet line 108 and outflow line 109 tolower or increase the level in the vat in response to fluctuationsduring a build by means of a two-way flow valve in the valve assembly131 that is actuated similarly by a command from the stereolithographysystem control computer in response to the sensing by sensor 87. Theliquid level sensor 87 takes a reading of the precise level in the vatbetween each layer. The resin may shrink when solidified. Displacementof resin by the platform and build as these are lowered may impact thelevel of resin in the vat. A useful pump for controlling resin levelduring a build is a metering pump, such as peristaltic pump 104, fordelivery of small, precisely controlled amounts of fluid and may takeseveral strokes to add or remove resin so that the level in the vat canbe closely controlled. A peristaltic pump can supply about 1 micron offluid volume over several strokes to provide precise control. Valveassembly 131 can also circulate resin from the vat 21 through line 110through valve assembly 131, line 111, bellows pump 102, line 113, andback into vat 21, if needed. This circulation feature can help preservethe quality of the resin in the vat 21 and prevent viscosity increases.It can best be employed between builds either automatically or operatorinitiated through the stereolithography control system's software.

It should be recognized that the focal plane of the laser beam emittedby the Omron sensor is the same whether at the resin surface or theplane of the recoater blade. A conventional beam profiler systememploying a detector array and establishing a Gaussian beam distributiondetermines the beam location and width of the laser beam. The system canchange the focal length of the beam using a 3-axis scanner that is selfcalibrating and permits customized blade gap settings for differentresins. Storage of this information over time will establish a libraryof data log files for particular resins in individual systems of theinvention.

It is useful to mark the resin containers with radio frequencyidentification tags (RFID technology) so as to ensure accurate resinreplacement and to avoid the costly error of mixing different resins. Anoperator can be alerted prior to connecting the resin vat to thesupplemental container if the resins are different and can obtainconfirmation of the correct resin.

Laser systems of the type typically used for stereolithography areuseful in the practice of the method and apparatus of the invention. Anx, y scanning laser employing mirrors controlled by galvanometers toposition the laser beam are useful. A scanning system 100 is illustratedin a highly schematic view in FIGS. 19, 20, and 21 applying energy tothe working surface 112 of the resin, the build plane, in apredetermined path to solidify a layer 115 of an object 117. A laserwindow normally isolates the laser and galvanometer systems from theprocess chamber, which is heated.

Dynamic beam deflectors can be used to generate more than one sequentialpath for the laser beam so that the laser can be used more effectively.To increase efficiency, a single laser can be used in connection withthe practice of the invention to provide energy to two or more separatestereolithography chambers 12, 13 (FIG. 1) and galvanometer systems forsimultaneous builds. While a three-dimensional object in one chamber isbeing recoated with a layer of fresh resin, the laser can be conductinga scanning exposure in the adjacent chamber so that the laser does notsit idle between recoats of a build.

The laser control system is capable of dynamically changing the laserfocus so that larger objects can be produced without a loss ofprecision. As shown in FIGS. 9 and 18, detector cells 89 located in therear of the chamber and mounted to the chamber elevator subassemblyframe 92 provide information for controlling the intensity, focallength, and spot size of the laser beam that is provided by scanner 100(FIG. 18) and is used to solidify the resin. As with the Omron sensor, a3-axis scanner is useful to change the focal length and spot size of thelaser so that the build is the same quality and precision whether in themiddle of the resin or at the outer edges of the vat.

FIG. 19 shows in perspective illustration the scanning exposure of thelaser in the x, y plane of the surface of the resin. The progress of thebuild is shown in FIGS. 20 through 23. It should be recognized that thesupport layers for the desired object are the first to be solidified. Asshown in FIG. 20 in a section through the chamber, the support platformis gradually lowered as cross-sectional layers 115 are solidified byapplication of the laser beam. The laser solidifies a layer, theelevator lowers the platform to provide a fresh layer of resin and therecoater levels the resin to provide one layer thickness. After multiplesequences of scanning exposure of the laser and recoating with resin,the platform has been lowered to a greater depth as shown in FIG. 21 anda single build object 117 has been completed. The elevator then removesthe build and platform from the resin to the unload position as shown inFIG. 22 in section and in FIG. 23 in perspective.

FIGS. 24 through 31 illustrate the sequence of steps involved inautomated offloading of a completed build and supporting platform and incompleting a second build. FIG. 24 shows a side view of astereolithography chamber of the invention having a completed buildobject 117 supported on a platform 30 and elevated for release of theplatform latch as discussed above. A perspective view of this stage ofthe completed build in the chamber is shown in FIG. 23. It should berecognized that the recoater blade 42 and carrier 44 are parked prior toelevation of the build out of the resin. Also shown in FIG. 24 is anauto offload cart 120 connected to a computer control 126 for carryingout the unattended platform swap by which a second build can occur. Cart120 has telescoping arm segments 123 and 125 (FIG. 25) for,respectively, supporting and conveying a drip tray 122 for offloadingthe build object 117 and platform 30 and for supplying a fresh platform124 for the vat.

The side sectional view of FIG. 24 illustrates that the offload cart isrolled into contact with the door 16 or 17 of FIG. 1 of astereolithography chamber from which the window has either been manuallyremoved or swung to the open position, and under a portion of the resinvat. As shown in FIG. 1, the doors have brushes defining an opening atthe bottom through which the rollers of an auto offload cart enter. Theauto offload cart should be docked with the vat so that the telescopingarms coordinate with the vat and elevator for a flawless platformexchange. FIG. 32 illustrates fittings 132 and 139 that can be used toensure docking to the resin vat. Docking is not automated, and isperformed by an operator who also connects the cart to the controllersystem 126 for the stereolithography system (FIG. 24). The window in thechamber door, 16, 17, (FIG. 1) is hingedly opened or removed by theoperator so that the automated build removal can proceed.

At the end of the build, the platform 30 and build object 117 areelevated sufficiently high to release latch 36 securing the platform.against tabs 33 and 35 to the forks and frame 24. A telescoping arm 123extends from the cart having a drip tray 122 thereon so that theelevator frame 24 is disposed above the drip tray (FIG. 25). Theelevator frame is lowered and the drip tray and forks are configured sothat the platform and build rest on the drip tray and the frame passesthrough (FIG. 26). Telescoping arm 123 is retracted and the build objectand platform are removed from the chamber to rest on the cart. Theelevator frame is then lowered to receive a fresh platform, latch 36still in the released position (FIG. 27).

Telescoping arm 125 is extended as shown in FIG. 28 and having a freshplatform 124 thereon. The elevator frame is then raised to engage andreceive this fresh platform and the telescoping arm is retracted (FIG.29). It should be recognized that the latch 36 securing the platform tothe elevator frame does not engage until the platform is loweredsufficiently, in reverse of the method by which the latch is opened.

Once the fresh platform is in place and the latch secured, the elevatorcan lower the fresh platform into the vat of resin and below the resinsurface for a determination, as discussed above, as to the amount ofresin that is required to be added for the second build (FIG. 30). Thesecond build is completed as the first, providing, as shown in FIG. 31,an offloaded first build object 117 and a second build object 130elevated on its platform above the resin vat.

Having described the apparatus of the invention in some detail, andturning now to a consideration of the process steps, FIG. 33 shows abasic now diagram for accomplishing an unattended build in a single vataccording to the invention. In the unattended build mode, the apparatusbuilds a first three-dimensional object, removes the completed buildobject from the vat and elevator, and completes a second, unattendedbuild. After the first build is removed, the apparatus installs a freshplatform on the elevator and adjusts the resin parameters as required,completes the second build, and removes the second build from the resinvat. It should be recognized that several objects can be built in abuild simultaneously in a single vat or in adjacent vats and that FIG.33 illustrates an unattended build of a single object in but one vat.Unattended builds can occur simultaneously in other vats in a multi-vatprocess.

At the process start, according to step 140 in FIG. 33, the humanoperator will have performed several functions. Having selected anunattended build mode, the operator will first need to input the objectrepresentation, typically using a CAD/CAM program for the objectrepresentation. The operator then determines the volume of resinrequired for the first build and whether the build volume is within thedesign limitations of the apparatus. For example, if the capacity of theapparatus includes building parts using up to 20 kilograms resin and nomore, then if the object selected requires more, the operator will needto select a different build mode. If the design capacity provides formaking a first and attended build, but not an unattended second build,then the unattended mode cannot be used.

The operator also verifies that a recoater blade is installed and isparked up and out of the way so as not to hit the resin vat wheninstalled. Once the resin vat is installed, then the operator shouldverify that the vat is correctly installed and that the vat containssufficient resin of the correct type. Normally, the vat will include anelevator subassembly, including an elevator attachment bracket, elevatorsupporting framework and forks, and a build platform secured by latch 36and tabs 33 and 35 to the forks. The entire vat and elevator subassemblyis rolled into the stereolithography chamber to engage the chamberelevator subassembly.

The relationship between the resin surface and the recoater blade can bemapped at this point or another point prior to the build and the datastored for use during the build. Once a particular resin is identified,the blade gap for the rein selected, and the level of the resinreproducibly controlled within the vat, then the map for theseconditions should be useful for the same apparatus over a period oftime.

In accordance with step 142, the operator installs the auto off-loadcart having once satisfied the initial requirements and verified that anunattended build is supported. To install the auto off-load cart, theoperator hingedly opens or removes the window on the chamber door sothat the telescoping arms of the auto off-load cart can extend into theprocess chamber for retrieving the platform and first build. Theoperator docks the auto off-load cart into the vat with the chamber doorclosed. The chamber is heated and to avoid disturbances to the process,the chamber door is kept closed. Wheeled feet extend from the autooff-load cart into the chamber through a cutout in the bottom of thechamber door that is covered with brushes to minimize debris and heatlosses. The vat and auto off-load cart are configured to maintain aconsistent position when docked, one with respect to the other, forautomated operation. The operator also makes sure the auto off-load cartis connected to the stereolithography system's computer for control ofthe automated operation.

Operators may change shifts at any point during preparation of theapparatus of the invention for the unattended build mode. Consequently.successful operation of the system often requires that the operatorsverify information about the system more than once. Thus, it is usefulto have the computer control prompt the operator to verify before thefirst build starts that an empty platform is in fact in place on theauto off-load cart for installation when the first build is completed.Alternatively, verification that a platform is properly in place can beaccomplished using appropriate sensors.

In accordance with step 144 the operator then causes the recoaterassembly and elevator to go to the start positions. The elevator islowered into the vat and is brought to a level just under the surface ofthe resin so as to define the working surface. The recoater assembly islowered to the resin to define the preselected blade gap between thebottom of the foot and the working surface of the resin.

At this time, just prior to the actual start of the laser and recoater,it is useful to prompt the operator to verify the operating parameters.The operator should verify that a build platform is actually installedon the forks. If the build were to start without a platform in place,the results in lost productivity and resin could prove costly. If theplatform is not in place on the elevator forks, then the operator shouldpark the recoater, raise the elevator to the platform release position,and install a fresh platform. Once the presence of a platform isverified, then the resin and chamber temperatures should be checked.Typically, temperature control is a computer controlled function that iscontinuously performed. Nevertheless, it is useful for the operator toverify that the temperature is correct prior to initiating a build. Theoperator should also verify that the vat has sufficient resin. Even ifthe capacity of the system is adequate for the build, the system shouldbe checked to verify that the vat contains the resin and that the resinlevel is between the preselected minimum and maximum levels in the tanknecessary for fine level control of the build plane.

The operator should also verify, in accordance with step 148, that thesupplemental resin containers contain sufficient resin for refilling thevat between builds and for fine level control during the builds. If notsufficient, then the operator should be prompted by the system, inaccordance with step 149, to replace the partially full containers withfull containers and to verify that the new containers contain the sameresin as is in the vat. One efficient method of verifying the resins arethe same is to run a radio frequency identification routine, or “RFID”routine. RFID tags can be included in the containers for automatedidentification prior to completing connection to the vat, after whichthe operator can complete installation if the resins are the same. Theuse of RFID tags on the containers and the vats permits data collectionon the system's resin and resin usage to occur via data flow from theparticular RFID reader on the elevator assembly for the vat and theindividual RFID readers on the smart couplers on the vat for eachcontainer.

If the above parameters have been met, then the build can proceed. Theoperator should turn on the recoater vacuum in accordance with step 150and adjust the resin level and resin and chamber temperatures as shownin steps 152 and 154 respectively. At this point, the resin level iswithin the preselected minimum and maximum levels and the level isadjusted within these levels to the precise level of the build planethat has been selected. Material is pumped into or removed from the vatby a metering pump interface with the two supplemental resin containersused for this purpose, and is automatically controlled in response to asensor.

The recoater blade prepares the working surface to receive the laser andthe actual stereolithography can now begin, in accordance with step 156,with preparation of the support layers. At this time, the operator'sattendance to the process is no longer needed and the build proceedsbased entirely on computer controlled functions. Typically, after eachlayer is solidified, the elevator will lower the platform to receive afresh coating of resin and raise the platform sufficiently for lasing ofthe next layer. Resin level is adjusted as needed depending on theamount of shrinkage due to solidification and displacement by theplatform and object below the surface of the resin. The recoater bladesweeps the surface between each layer to prepare the working surface andthe build proceeds in accordance with step 158. Steps 156 and 158 mayoverlap.

Once the object is completed, the build is stopped, and the laser isturned off, then the system proceeds without an operator in attendanceto exchange platforms. The system parks the recoater assembly inaccordance with step 160 up and out of the way of the elevator forks soas to enable the elevator to move completely out of the resin vat withthe build on the platform. The elevator is raised to the unload positionin which the latch securing the elevator platform is released and theplatform can be removed from the forks. The elevator forks, buildplatform, and build are now positioned over the vat and the unused resinstill in contact with the forks, platform, and build object then drainsinto the vat in accordance with step 164. After a sufficient dwell timeto provide an effective drain, the auto off-load cart removes theplatform and completed and drained build object in accordance with step166. Computer control extends a set of telescoping arms from the autooff-load cart underneath the elevator forks so that the forks can belowered to deposit the platform and build on the telescoping arms of theauto off-load cart. A drain pan normally is desirable on the telescopingarms so that the platform and completed build object are deposited ontothe drain pan on the telescoping arms. The telescoping arms retract toremove the platform and build object from elevator forks and thestereolithography chamber.

After the first build is removed from the chamber, the elevator movesthe forks into position to receive a fresh platform in accordance withstep 168. Telescoping arms again extend from the auto off-load platform.Depending on the configuration of the auto off-load cart, the cart mayhave one or two sets of telescoping arms. If two, then the first buildobject and platform remain in place outside the chamber. If one set,then the first build object again enters the chamber and the area abovethe vat and is positioned above the forks. The elevator forks are raisedto engage and receive a fresh platform from the telescoping arms inaccordance with step 170 and then the telescoping arms are removed, thefirst build object and platform to be stored with the auto off-load cartuntil the second build object is completed and the operator returns tothe system.

Once the fresh platform is installed, the system returns to repeatseveral of the previous steps as shown in step 172. The elevator lowersthe fresh platform into the resin, step 171, and brings the platform tothe appropriate level. The system automatically and in response tosensors refills the vat and adjusts the resin levels and temperature andsweeps the working surface to prepare for the second build. The secondbuild proceeds and, when completed, the recoater is parked and theelevator removes the second build and platform to an upper position outof the vat.

When the operator returns, the first and second builds are complete, thefirst build object is stored outside the chamber on the auto off-loadcart, and the second build object is within the chamber, drained abovethe vat and ready to unload. It should be recognized that a single buildis similar in the steps of building the object, and that the autooff-load cart may or may not be installed as desired. In either case,for a single build the system is directed to shut down after the firstbuild. The system of FIG. 1 is a dual chamber system, and so twounattended builds can be performed using a single laser and separatescanners and auto off-load carts for each chamber to provide two buildsoutside the chamber, one on each cart, and two inside, one in eachchamber.

Many modifications and other embodiments of the invention set forthherein will come to mind to one skilled in the art to which thisinvention pertains having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1. A method for producing three-dimensional objects from a liquid resinby curing selected portions of the liquid resin layer-by-layer, whereina layer is defined along an x-axis and an y-axis and wherein a layerthickness is defined along a z-axis, the method comprising: a) moving arecoater along the y-axis across a working surface of the liquid resin,wherein the recoater is operatively connected to a controller; and b)adjusting the recoater about a theta axis as the recoater moves alongthe y-axis, wherein the theta axis is parallel to the y-axis.
 2. Amethod according to claim 1, wherein moving the recoater along they-axis comprises moving a recoater assembly that includes the recoaterand a carrier to which the recoater is operatively connected.
 3. Amethod according to claim 2, wherein the recoater comprises a vacuumassisted recoater and includes a vacuum port for engaging a source ofvacuum.
 4. A method according to claim 2, wherein adjusting the recoaterabout the theta axis corrects for machine errors of a rapid prototypingand manufacturing apparatus of which the recoater assembly in included.5. A method according to claim 4, wherein correcting for machine errorscomprises correcting for unevenness in mechanical systems of the rapidprototyping and manufacturing apparatus of which the recoater assemblyis included.
 6. A method according to claim 1, wherein adjusting therecoater about the theta axis further comprises adjusting the recoateralong the z-axis.
 7. A method according to claim 1, wherein adjustingthe recoater about the theta axis keeps the recoater generally parallelto the working surface of the liquid resin.
 8. A method according toclaim 1, wherein adjusting the recoater about the theta axis moves atleast one end of the recoater along the z-axis relative to the workingsurface of the liquid resin.
 9. A method according to claim 1, whereinadjusting the recoater about the theta axis is controlled by thecontroller in response to predetermined data for adjustment.
 10. Amethod according to claim 9, wherein the predetermined data foradjustment is based upon pre-measured blade gaps between the recoaterand the working surface of the liquid resin.
 11. A method according toclaim 1, wherein curing selected portions of the liquid resin comprisesscanning a laser beam on the working surface of the liquid resin.
 12. Amethod for producing three-dimensional objects from a liquid resin bycuring selected portions of the liquid resin layer-by-layer, wherein alayer is defined along an x-axis and an y-axis and wherein a layerthickness is defined along a z-axis, the method comprising: a) providinga housing having a frame, a container of liquid resin within thehousing, a source of energy for curing selected portions of the liquidresin, a build platform within the container to support thethree-dimensional object, an elevator for moving the build platformalong the z-axis, a recoater extending generally along the x-axis forleveling a working surface of the liquid resin in the container, and acontroller operatively connected to the source of energy, the elevator,and the recoater; b) determining a distance between a portion of arecoater and the working surface of the liquid resin in the container atmultiple locations along the x-axis and y-axis, wherein the distancesfor the respective locations define predetermined data for adjustment ofthe recoater; c) moving a recoater along the y-axis across the workingsurface of the liquid resin to level the working surface for at leastone layer of the liquid resin from which selected portions are cured todefine a layer of the three-dimensional object; and d) adjusting therecoater about a theta axis as the recoater moves along the y-axis inresponse to the predetermined data, wherein the theta axis is parallelto the y-axis and wherein adjusting the recoater about the theta axiskeeps the recoater generally parallel to the working surface of theliquid resin.
 13. A method according to claim 12, wherein determining adistance between a portion of a recoater and the working surface of theliquid resin comprises measuring a blade gap between a foot of therecoater and the working surface of the liquid resin.
 14. A methodaccording to claim 13, wherein the blade gap is measured for at leasttwo locations along the x-axis for each of at least two positions of therecoater along the y-axis.
 15. A method according to claim 12, whereinadjusting the recoater about the theta axis corrects for unevenness inat least one of the container and frame, wherein the recoater is movedalong the y-axis on at least one of the container and frame.
 16. Amethod according to claim 12, wherein adjusting the recoater about thetheta axis further comprises adjusting the recoater along the z-axis.17. A method for producing three-dimensional objects from a liquid resinby curing selected portions of the liquid resin layer-by-layer, whereina layer is defined along an x-axis and an y-axis and wherein a layerthickness is defined along a z-axis, the method comprising: a) moving arecoater along the y-axis across a working surface of the liquid resin,wherein the recoater is operatively connected to a controller; b)adjusting the recoater about a theta axis as the recoater moves alongthe y-axis, wherein the theta axis is parallel to the y-axis; and c)raising and lowering the recoater along the z-axis as the recoater movesalong the y-axis to maintain a constant distance at each end of therecoater from the working surface of the liquid resin.
 18. A methodaccording to claim 17, wherein adjusting the recoater about the thetaaxis and raising and lowering the recoater correct for unevenness inmechanical systems of a rapid prototyping and manufacturing apparatus ofwhich the recoater is included.
 19. A method according to claim 17further comprising determining blade gaps between a foot of a recoaterand the working surface of the liquid resin at multiple locations todefine predetermined data, wherein adjusting the recoater about thetheta axis and raising and lowering the recoater are controlled by thecontroller in response to the predetermined data.
 20. A method accordingto claim 17, wherein curing selected portions of the liquid resincomprises scanning a laser beam on the working surface of the liquidresin.